A difficult winter for Paul Nicholls became significantly worse when he learned on Thursday that Tidal Bay would be unable to run in the Grand National. The horse had been heavily backed this week after publication of the weights to be carried but a stress fracture in a hind leg will prevent him from being ready in time for the race on 6 April.

It was typical of Nicholls' open approach that he rushed the news out as soon as possible but, after issuing a statement, he made himself unavailable, presumably in a state of boiling frustration. He had suffered a similar setback in December when two other major talents in his yard, Big Buck's and Al Ferof, were found to be injured on the same day.

Tidal Bay has acquired a large and slightly perverse fan club in his seven-year career, attracted by both his enormous talent and his apparent reluctance to use it. Over one particularly unproductive period of three and a half years he achieved only one victory.

But Nicholls appeared to have helped the horse overcome his quirks after he took him on from his former trainer, Howard Johnson, who was banned for four years in 2011. Tidal Bay won three of his last four races, including Ireland's Lexus Chase, and became a popular choice for the National after it emerged on Tuesday that he would have less weight to carry relative to his rivals than had been expected.

"He was the best-backed horse for the National this week," said David Williams of Ladbrokes, who shortened him from 25-1 to 14-1 third-favourite in two days. "And we also saw plenty of money for him last week for the World Hurdle when the trainer suggested that might be his Cheltenham Festival target.

"Still, we should keep this in perspective. It's not mega-money we're talking about, much less significant than when Binocular was ruled out of the Champion Hurdle two days beforehand."

It appears Tidal Bay's injury may have been the same one that caused him to miss a race in late January through lameness. Nicholls says that x-rays taken at the time failed to show anything and the horse was returned to light exercise this week. But his work rider became concerned when he was asked to do more on Wednesday.

Tidal Bay was dispatched to a vet in Newmarket, who discovered the injury by use of an MRI scan. Though said to be "tiny", the fracture requires a month's box rest. Tidal Bay, who is now 12, may have run his last race, though his owner, Graham Wylie, expressed a hope that he might return next season.

Many bookmakers cut their odds about the National favourite, Prince De Beauchene, though some 12-1 remains. But Tidal Bay's exit means that horse will now have close to top weight, perhaps having to shoulder as much as 11st 8lb, depending on other possible withdrawals.

Aintree racecourse was drawn into the horsemeat scandal on Thursday when it emerged that it has a contract for removal of dead horses with the owner of an abattoir raided by the Food Standards Agency on Tuesday. Peter Boddy has offered no comment since his slaughterhouse in Todmorden had production suspended and paperwork seized when FSA officers and police attended this week.

A spokesman for Aintree said: "The racing industry takes every possible course of action to ensure that horses, fatally injured on a racecourse, cannot enter the food chain. By the time these carcasses are returned to the disposal organisation's premises, they are totally unsuitable for consumption. Indeed, it is illegal for horses humanely put down by injection on the [track] to enter the food chain."